Written by Walt Powell, Professional Engineer
Sometimes an old substation will have old oil filled transformers that have no gauges. These are usually 500 kva to about 2000 kva transformers. We are not referring to pole top type transformers. Some Utilities used oil filled transformers with no accessories to save costs. They would consider these transformers to be small and basically disposal. Many of these substations have been sold by Utilities to the consumer. The consumer gets a cheaper primary rate and owns the substation, along with the responsibility to take care of it. Sometimes we are asked how to determine the oil level in a transformer that does not have an oil level gauge, without turning the transformer off. We safely feel the cooling tubes and the tank. If the tubes are cool and the tank is hot, it is low on oil. If the oil is properly circulating through the cooling tubes, the tubes will also be warm. Not as warm as the tank, but fairly close. Caution, only a qualified electrician or electrical engineer should do this. Stay away from energized parts and make sure the transformer tank is properly grounded before you touch it. Protect yourself from shock hazard and from an electrical arc blast hazard. This may well require PPE. Do not touch anything else while touching the transformer tank.
MIDWEST is frequently asked if it is safe to take an oil sample from a sample valve under the secondary cables of a pad mount transformer while the transformer is still energized? No, it is not safe. Do not do it. We think it is extremely dangerous. This is the location of possibly one of the most dangerous arc flash hazards in a facility. You can’t wear enough PPE to protect yourself. Keep away from the secondary. Just opening the door to inspect it can be very dangerous. In addition, you would be exposed to unsafe shock hazard. Our recommendation is to sample the transformer during a scheduled outage. We know very well in years past this was common practice for many service companies. Those days are gone. As they should be.
It’s starting to catch on this energy efficiency stuff. For once, it seems, the numbers tell the story.
A man in Iowa buys a former manufacturing facility and changes it to a warehouse facility. He no longer needs the amount of power from the production days as the facility is now used to store portable generators. Building load is now mainly just for lighting. Starting in January 2007, the Federal Energy Policy Act of 2005 mandates new minimum energy efficiency standards for low voltage dry type transformers per the NEMA TP-1 2002 Standard.
The new owner swaps out the old 500 KVA dry type transformer which powered the building for a new Jefferson 150 KVA 480/240 dry type transformer at a purchase cost of $3,375.00. Given equal loads, the new Jefferson high efficiency 150 KVA transformer translates into substantial savings due to lower “no load core loss”. The new transformer saves up to approximately $175.00 per month in electricity used. The recovery cost break even point at that rate was 19 months. Another important factor when considering a new replacement transformer is the size of the transformer footprint. The new Jefferson had an 80% smaller footprint even though the transformer KVA capacity was reduced by 70%. These are numbers you can depend on. “Things are in the saddle…ride mankind ride.”